The present invention relates to a honeycomb segment and a honeycomb structure using the honeycomb segment.
A honeycomb structure is incorporated in an exhaust gas system or the like of a diesel engine as a trapping filter for exhaust gas, for example, as a diesel particulate filter (DPF) in order to trap and remove particulate matter contained in exhaust gas from a diesel engine or the like. Such a honeycomb structure has a problem of having defects such as causing cracks and the likes by thermal stress due to uneven temperature rise in the whole honeycomb structure upon use (upon trapping and removing particulate matter) and upon regeneration (upon removing, by combustion, particulate matter accumulated inside a filter in order to reduce an increase in pressure loss due to particulate matter accumulated inside the filter in the course of time). From the viewpoint of solving such a problem, there is provided a honeycomb structure having reduced thermal stress by forming a honeycomb segment joined body having a plurality of honeycomb segments unitarily joined with one another at their joint faces by means of a bonding material layer.
However, since a honeycomb structure made of silicon carbide (SiC), whose use is expected because it has an advantage of excellent thermal resistance, has a high thermal expansion coefficient in comparison with a cordierite honeycomb structure and a disadvantage of inferior thermal shock resistance, it has a problem of difficulty in making good use of the advantage sufficiently. In addition, according to recent increase in size of a filter, thermal stress generated upon use or regeneration has been increased remarkably, and thereby frequency and extent in generation of a defect based on thermal stress have rapidly fallen into a serious state.
To cope with such a problem, there is disclosed a method for manufacturing a ceramic structure (honeycomb structure), the method being characterized by including a step of forming an adhesive paste layer (bonding material layer) on a side face of a porous ceramic member (honeycomb segment) so as to cover 60% or more of the total area of the side face and a step of piling up ceramic blocks by repeating a step of laminating other porous ceramic members (see Patent Document 1).
However, in the ceramic structure (honeycomb structure) disclosed in Patent Document 1, its rigid joint structure all the more increases thermal stress generated from a temperature gradient, and the joint member has a large thermal capacity and a low temperature rise or fall rate in comparison with a porous ceramic member, which easily increases a temperature gradient inside the filter. Therefore, there is a problem of insufficiently inhibiting a defect due to thermal stress from being generated.
In addition, inferiority of chipping, cracks and the like are prone to occur intensively on cells at the four corners of the honeycomb segment upon conveyance of the honeycomb segment or upon handling the honeycomb segment before joining. Since it is difficult to decrease inferiority of honeycomb segments even with careful handling of the honeycomb segments, it causes deterioration in productivity or a yield of a ceramic structure (honeycomb structure) as a finished product.
Patent Document 1: JP-A-2002-219317
The present invention has been made in view of the above problems and objects to provide a honeycomb segment capable of improving productivity and a yield of a honeycomb structure. Because occurrence of a chip or a crack during handling before joining honeycomb segments can be reduced by enhancing mechanical strength of the honeycomb segments constituting the honeycomb structure.